This contractor will be a clinical center for the collaborative clinical trial, Cardiac Arrhythmia Treatment Study (CATS). Th primary objective of this contract is to see if effective drug treatment of frequent ventricular premature depolarizations in post-myocardial infarction patients will reduce the incidence of sudden cardiac death; secondary objectives are to (1) assess the impact of treatment on all-cause mortality, (2) evaluate adverse drug effects, (3) examine the clinical course of the disease in the control group, and (4) conduct selected substudies to clarify the disease process and the mechanisms of drug efficacy. A three-year recruitment period is designed, following a ten-month planning phase. Follow-up will continue two years beyond patient recruitment.